The contrast between LED street lights and traditional sodium lamps is not that simple.

LED light principle:

LED (Light Emitting Diode), a light-emitting diode made of a Group III-IV compound, is a solid-state semiconductor device that directly converts electricity into light. The heart of the LED is a semiconductor wafer. The semiconductor wafer consists of three parts, one part is a P-type semiconductor, in which the hole dominates, and the other end is an N-type semiconductor. When a current is applied to the wafer through a wire, electrons and holes are pushed into the vector sub-well. In the quantum well, the electrons recombine with the holes, and then the energy is emitted in the form of photons. This is the principle of LED illumination. The wavelength of light, which is the color of light, is determined by the material that forms the PN junction.

The principle of light emission of high pressure sodium lamp:

The high-pressure sodium lamp uses an electric arc to generate an arc between the electrodes at both ends of the arc tube. Due to the high temperature of the arc, the sodium amalgam in the tube is evaporated by heat into mercury vapor and sodium vapor, and the electrons emitted by the cathode move toward the anode during impact. The atom of matter, which is energized to produce ionization or excitation, and then returns to the ground state from the excited state; or from the ionized state to the excited state, and then back to the ground state infinite loop, at which time the excess energy is released in the form of optical radiation. It produces light.

The high-power LED street lamp is a new type of illumination method for illuminating the LED group by DC low voltage, which has the characteristics of high brightness, good color rendering, etc. In addition, since the input of the LED street lamp is low voltage DC, it can The combination of solar energy makes solar LED street lights a potential for future road lighting.

1. About energy efficiency analysis and comparison

The lighting installation power of both should be compared in accordance with the same illumination (brightness) level and close lighting quality standards. Because the high-power sodium lamp high-power lamp (250~400W) has high luminous efficiency, it can reach 130~1401m/W, while the low-power lamp (100~150W) has about 40~1001m/W, and the current high-power LED The street lamps use 1W LED tubes, and their light effects are similar. Therefore, it is necessary to analyze the high-power street lamps and low-power street lamps separately.

(1) High-power (≥250W) street light: High-pressure sodium has high light efficiency. Considering three factors such as ballast loss, lamp efficiency and track utilization, if the overall efficiency is 0.55, the effective light efficiency of the sodium lamp is about 70~751m/W; and the effective light effect of LED street lamps is currently about 621m/W in the US, and the best domestic enterprises have reached 56~581m/W. Therefore, we think that for high-power street lamps, LEDs are currently less energy efficient than sodium lamps.

(2) Low-power (≤150W) street light: The effective light efficiency of the sodium lamp (included in the comprehensive efficiency of 0.55) is about 45~551m/W, while the LED is still calculated according to 56~581m/W, the LED can achieve energy saving compared with the sodium lamp. %~20%, up to 30%. From the above analysis, it can be seen that the LED street lamp can save 10%~30% energy compared to the sodium lamp when the power is small (≤150W) for the branch, and the high power is still not comparable to the energy efficiency of the sodium lamp. Therefore, those who generally claim that LED street lamps are more energy efficient than high-pressure sodium lamps, and even save 50%, 60%, etc., are obviously exaggerated and speculative. We should adhere to the scientific analysis and the principle of seeking truth from facts, otherwise it will easily mislead users and the masses.

2. Analysis of the effect of light source color on road lighting

The color temperature (Tcp) of the high pressure sodium lamp is about 2100K, which is a warm color temperature. The color rendering index (Ra) is only 23~25, and the color rendering is low. The color temperature of the LED street lamp is more than 5300K, which is a cool color temperature. The product has a Ra of 70~80 and good color rendering. As a fast track, main road, and yellow light of the motor vehicle, it is better to see the road surface at a distance of about 90~160m in front, which is better than white light, especially for foggy and dusty air conditions. More advantage. For roads such as sidewalks, commercial pedestrian streets, residential quarters, etc., the color rendering of LEDs is better than that of sodium lamps, which distinguishes people's conditions more clearly and has advantages.

3. Economic analysis and comparison

High-pressure sodium lamps, each set is about 1200~1500 yuan; currently LED street lights, according to the size of the power, the price difference is large, about 4000~8000 yuan. As far as the status quo is concerned, LED street lights are obviously too expensive, and the price is as high as 3 to 5 times. For example, LEDs with less than 150W can save 10%~30% energy, and each lamp saves about 50~150KWh per year. It is impossible to recover the cost of purchasing lamps. It can only be expected that in the next few years, the LED development trend will see its price gradually decline, energy efficiency will be further improved, and then its economic performance will be compared.

4, life analysis

The comparative service life should be based on the life of the lamp. High-pressure sodium lamps include light sources, electrical accessories (mainly ballasts, triggers) and lamps, sodium lamps for street lamps with an average life of 3 to 5 years, and energy-saving magnetic ballasts for no less than 20 years. However, there is no experience in the service life of LED street lamps. The existing enterprises are known as 50,000 and 60,000 hours, and there is no reliable basis. The requirements set by the US Energy Star are divided into two grades of no less than 35000h and 25000h, mainly because the LED chip has a long life, but it has a great relationship with many factors such as temperature and heat dissipation after packaging, and there are also electronic circuits for driving circuit devices. Component life issues, such as capacitors are often only 8000h to 10000h. Therefore, as a whole, the service life of LED street lamps cannot be compared with that of sodium lamps.

5, maintain performance comparison

Users represented by the urban street lamp management department are more concerned about the maintenance performance of street lamps. According to the analysis, the maintenance performance of the sodium lamp is good, the lamp needs to be scrubbed, there is no need to replace it, the ballast is rarely replaced, and the light source is replaced once every 3 to 5 years, which is also very convenient. LED street lights, LED tubes, modules (including lenses, etc.), power supply devices, etc., are more likely to cause damage to components and components, and maintenance and replacement are also difficult. It is likely to be replaced as a whole, and the cost is high. solve. LED street lights have no standard to follow, which is unfavorable for bidding, ordering, and use and maintenance. In summary, we believe that LED street lights are new things that have emerged in recent years. With the development of the LED industry, there will be greater development and broad prospects. However, there are still many problems in the current application status. Although there are a few companies engaged in the research, development and production of LED street lamps, they have made great efforts to solve some technical problems and promote the advancement of this product. They are not the elite of the industry; But as a whole, the level, quality, unevenness and difference of LED street lamp products are very large. There are no standards to standardize. Some have quick success, some products are not efficient, the heat dissipation problem is not handled well, the light decay is very large, and the service life is not long. There is no reasonable lighting for the lamps and lanterns, and the promotion and use requirements cannot be met. We hope that scientific research, teaching, design units, use units and production enterprises work together to solve various technical problems, improve product levels, formulate and improve a series of standards, and prepare for the promotion and application. In the promotion and application, we should adhere to the step-by-step approach, starting from the pilot, summing up the experience, and continuously improving; from the application of small power LED street lamps to the branch roads, residential roads, and then to the main roads, high-power street lights, and gradually advance. No matter what kind of light source or lamp is used, it should meet the requirements of “City Road Lighting Design Standards” (CJJ45-2006), including brightness, illumination, uniformity and other quality indicators. Adhere to seeking truth from facts, avoid excessive exaggeration, compare bogey to raise yourself, and avoid pressing down on others, adhere to lighting quality, photo (light) level, adhere to the combination of technology and economy, apply energy and environmental protection, prevent excessive hype, for users Service, responsible for the user, do not mislead the user, but also a real face of the user. Don't say "replace" what light source. It should be improved after several years or years, in order to become a high-quality, high-efficiency new light source and lamp in road lighting for users to choose. Let the user speak and let the effect be evaluated. Luminous efficiency: The unit is lumens per watt Lm/w. That is, the ability of an electric light source to convert electrical energy into light energy, expressed as the luminous flux emitted divided by the amount of electricity consumed.

6, luminous efficiency

The luminous efficiency of the LED light source is currently about 75 Lm/w in foreign countries and Japan, and about 65 Lm/w in domestically produced LEDs. The luminous efficiency of the high-pressure sodium lamp source is about 100 Lm/w, and the luminous flux emitted per w is 25 to 35 Lm/w higher than that of the LED. The luminous efficiency of the 400w high pressure sodium lamp is as high as 120Lm/w.

7, fogging

In the road lighting, there is a big misunderstanding about the penetration of LED street lamps for heavy fog. Most people have always believed that the penetration of LED street lights is lower than that of traditional lighting sources, which is a misunderstanding. Most people mostly see some information from the network or see some sensory feelings on the road, and do not make scientific evaluation and analysis, so that the light penetration of LED street lamps is poor. A scientific analysis of this situation will be made in this paper.

We all know that the range of visible light is between 380 nm and 780 nm, and the light in this range is acceptable and recognizable by the human eye. We believe that all luminaires have a value for use only in the light range of this band. This range is unrecognizable to the human eye. The analysis of penetration in this paper is also only carried out within this range. It can be seen from the spectrum that the spectrum of the LED is much more comprehensive than that of the sodium lamp. The peaks of both are at 580 nm, and the blue portion of the LED only accounts for about 6% of the total luminous flux, while the sodium lamp has almost no. The red light area of ​​the LED is distributed more widely than the high pressure sodium lamp.

8, performance comparison:

Performance comparison of high pressure sodium lamp and LED light source

(1) Comparison of service life

The LED lamp is a kind of semiconductor diode, and its light source has a very long theoretical life (provided that it meets the L70 light decay standard within the specified temperature range), but the overall life of a lamp is not simply the life of the light source, and the lamp also includes a lens. Part of the impact. Therefore, the life of the final luminaire should be limited to the shortest life component of all luminaire components. When the luminous flux is attenuated to 30%, its lifetime reaches 50,000 hours, while the life of the metal halide lamp is 6000-12000 hours, and the life of the high pressure sodium lamp is 20,000 hours.

(2) Comparison of lighting effects

1 color rendering index LED white light: 1 LED color temperature is 3500-7000K; 2 color rendering index is 80-93. Traditional high-pressure sodium lamp: 1 high-pressure sodium lamp color temperature is 2000-2500K; 2 color rendering index is 20-30. Through the above comparison results, it can be seen that the high-pressure sodium lamp has a low color rendering index, poor color rendering, and poor color reduction of the object itself, which is not conducive to judging the depth of the surrounding environment; the LED light source has a high color rendering index and good color rendering, which is good. The actual color of the restored object, but the white light is cold. Look at the high pressure sodium lamp, which is closer to natural light. At present, the efficacy of LED lamps is slightly better than that of sodium lamps. With the development and maturity of LED technology, the luminous efficacy of lamps will be greatly improved.

2 dimming function: LED light has a perfect dimming function. The LED lamp's light output is proportional to the operating current, so it can be dimmed by reducing the current. In addition, since the LED lamp is not frequently damaged by frequent switching, the LED lamp can also be dimmed by a pulse width adjustment method, and the luminous intensity of the LED lamp can be effectively adjusted by adjusting the duty ratio of the voltage and the operating frequency.

(3) Light utilization rate, luminous rate

The luminous flux loss of the LED light source is minimal, unlike the conventional light source, the LED light is a half-space light source. The high-pressure sodium lamp is a light source that emits light in a full space. It is necessary to redirect the outgoing light of one half space to the reflector of the other half space, and inevitably absorb the light and block the light source itself. The use of LED lights as a light source does not have this loss, and the utilization ratio of light is also higher than that of high-pressure nano lamps. LED lamps currently operate at 65-100 lumens per watt, while high pressure sodium lamps can reach 140 lumens per watt. The spectrum of the high-pressure sodium lamp is concentrated in yellow, and the color temperature is 2000-2500K. A very big problem with sodium lamps is that the illumination of sodium lamps is very poor. When the sodium lamp is in working condition, the temperature inside the lamp cavity should exceed 150 degrees, and the temperature of the LED lamp is 30% of the high pressure sodium lamp. In the non-working state, because of the negative pressure, a lot of dust and insects are sucked in, which greatly affects the light output of the sodium lamp. Effect and longevity. The LED is relatively stable.

(4) Comparison of energy saving and environmental protection

LED lights are energy efficient and ultra low power consumption. White LEDs consume only 1/10 of the energy of incandescent lamps and 1/4 of energy-saving lamps. And the light source of the LED lamp does not contain harmful metallic mercury. The high-pressure sodium lamp light source contains metallic mercury, metallic sodium (which becomes mercury vapor and sodium vapor after being energized), and has a short life (relative to LED), and subsequent waste disposal is environmentally polluting. The LED lamp has good shock resistance and convenient transportation. Solid state package, which is a type of cold light source. So it is very convenient to transport and install.

(5) Comparison of construction and cost

LED luminaires generally have a relatively good graininess, and their illuminating positions are relatively concentrated. Therefore, the LED needs to be better designed on the uniform light, and the point light source is extended as a surface light source as much as possible to improve the comfort of the eyes. Then there are many products that do LED dimming to save energy. At present, the LED street lamps designed and manufactured by most manufacturers are extremely heavy, often exceeding 10 kg. Such a large self-weight often makes the poles overload, reducing their wind resistance. Most LED luminaire manufacturers have designed LED luminaires to be replaceable, that is, to directly replace existing luminaires. The LED current is increased to reduce the number of wicks while maintaining the brightness to save cost, or to compress the PCB area, or to reduce the safety components.